U.S. patent number 5,531,920 [Application Number 08/315,782] was granted by the patent office on 1996-07-02 for method of synthesizing alkaline metal intercalation materials for electrochemical cells.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Zhenhau Mao, Dee Newton.
United States Patent |
5,531,920 |
Mao , et al. |
July 2, 1996 |
Method of synthesizing alkaline metal intercalation materials for
electrochemical cells
Abstract
A method for preparing an alkaline metal transition metal oxide
charge storage material for electrochemical cells. The material may
be used in a lithium rechargeable electrochemical cell along with a
conventional lithium intercalation electrode. The material may be
prepared by providing a transition metal hydroxide and reacting it
with a alkaline metal containing oxidizing agent. The ratio of the
transition metal to the alkaline metal should be approximately
0.5:1 to 1.2:1.
Inventors: |
Mao; Zhenhau (Coral Springs,
FL), Newton; Dee (Sunrise, FL) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
23226033 |
Appl.
No.: |
08/315,782 |
Filed: |
October 3, 1994 |
Current U.S.
Class: |
252/182.1;
429/224; 429/223; 423/599; 423/596; 429/231.1; 429/231.2;
429/231.3; 429/221; 423/594.15 |
Current CPC
Class: |
H01M
4/505 (20130101); H01M 4/463 (20130101); H01M
4/485 (20130101); H01M 4/405 (20130101); H01M
4/525 (20130101); H01M 4/131 (20130101); H01M
10/052 (20130101); Y02E 60/10 (20130101); H01M
4/44 (20130101) |
Current International
Class: |
H01M
4/48 (20060101); H01M 4/50 (20060101); H01M
4/52 (20060101); H01M 4/40 (20060101); H01M
4/44 (20060101); H01M 4/58 (20060101); H01M
4/46 (20060101); H01M 004/88 () |
Field of
Search: |
;252/182.1
;429/218,221,223,224 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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556555 |
|
Jan 1993 |
|
EP |
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6044971 |
|
Feb 1994 |
|
JP |
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Other References
Understand the Disordered Structure of LiMnO.sub.2 Prepared at Low
Temperatures, Reimers, et al, Dept. of Physics, Simon Fraser
University, Burnaby, B.C. Canada V5A 1S6. .
Improved Capacity Retention in Rechargeable 4V
lithium/lithium-manganese oxide (spinel) cells, Gummow, et al, Div.
of Materials Science, Jan. 20, 194. Elsevier, Solid State Ionics 69
(1994) 59-67. .
Lithium Batteries: New Materials, Development & Perspectives,
C. Pistoia, Elservier, New York (1994). .
Lithium Batteries: New Materials, Developments & Perspectives,
Industrial Chemistry Library, vol. 5, pp. 417-456. .
Preparation of High Surface Area EMD and 3-Volt Cathode of
Manganese Oxides, M. Yoshio, IBA New Orleans Mtg. Oct. 9, 1993.
.
Ohzuku et al. J. Electrochem Soc 140 (7) 1993 1862-1870. .
Ohzuku et al. Chemistry Express 6 (3) 1991 161-164. .
Ohzuku et al. Chemistry Express 5 (10) 1990 733-736..
|
Primary Examiner: Jordan; Charles T.
Assistant Examiner: Handee; John R.
Attorney, Agent or Firm: Massaroni; Kenneth M.
Claims
What is claimed is:
1. A method of fabricating an alkaline metal intercalation,
transition metal oxide material of the formula:
wherein A is an alkaline metal selected from the group of Li, Na,
K, and combinations thereof, TM is a transition metal selected from
the group of Ti, V, Mn, Cr, Fe, Ni, Co, and combinations thereof,
and wherein 0.5.ltoreq.x.ltoreq.1.2, said method comprising the
steps of:
combining a transition metal hydroxide of the formula TM(OH).sub.2
with an alkaline metal-containing oxidizing agent selected from the
group of Li.sub.2 O.sub.2, LiNO.sub.3, LiClO.sub.4, Na.sub.2
O.sub.2, K.sub.2 O.sub.2, and combinations thereof, in the presence
of a liquid organic solvent;
removing said organic solvent to collect a powdered alkaline metal
intercalation transition metal oxide material; and
calcining said powdered material in an oxygen free, inert gas
atmosphere.
2. A method as in claim 1, wherein the step of providing a
transition metal hydroxide includes the further steps of:
providing a transition metal containing precursor material in
solution;
adding a basic oxidizer to said transition metal containing
precursor material solution, said basic oxidizer having the formula
AOH, where A is an alkaline metal or NH.sub.4 --, and where the
ratio of transition metal to alkaline metal is approximately 1:2,
to form a precipitate; and
collecting said precipitate.
3. A method as in claim 2, wherein the step of adding an oxidizing
agent includes the further step of adding sufficient oxidizing
agent to said solution to have a pH of approximately 10.
4. A method as in claim 2, including the further step of providing
LiOH as said basic oxidizer.
5. A method as in claim 1, wherein the transition metal hydroxide
is Mn(OH).sub.2.
Description
TECHNICAL FIELD
This invention relates in general to the field of electrodes for
electrochemical cells, and in particular to methods of synthesizing
said electrodes.
BACKGROUND OF THE INVENTION
Numerous first transition metal oxide materials have been
intensively investigated during the past decade for use as the
positive electrode in rechargeable lithium batteries. These
materials which may be classified as either lithiated or
unlithiated metal oxides have been investigated because of their
high gravimetric energy density.
Unlithiated first transition metal oxides include compounds such as
V.sub.2 O.sub.5, V.sub.6 O.sub.13, TiO.sub.2 and MnO.sub.2. These
materials may be coupled with negative materials to form an energy
storage device such as a battery. The negative materials are
limited, however, to active lithium containing materials such as
metallic lithium and/or lithium alloys. Unfortunately, lithium and
lithium alloys are not preferred for many applications because of
their volatility in ambient conditions. Further, lithium poses many
difficulties for electrode material processing and cell
fabrication, since all the processes must be carried out in an
inert environment.
Lithiated first transition metal oxides such as LiCoO.sub.2,
LiMn.sub.2 O.sub.4, and LiNiO.sub.2, are positive electrode
materials. These materials may be coupled with a negative electrode
material to form a battery. Preferred negative electrode materials
include metals such as Al, Bi, and Cd, and a lithium intercalation
materials such as graphite. Metallic lithium and/or lithium alloys
are not required as in unlithiated transition metal oxides.
Accordingly, both the positive and negative electrodes can be
processed and fabricated without inert environments. Therefore,
lithiated metal oxides are more desirable as the positive material
than unlithiated metal oxides.
Among lithiated first transition metal oxides, LiMn.sub.2 O.sub.4
is most attractive because it is least expensive, and is
environmentally benign. Unfortunately, the gravimetric capacity of
LiMn.sub.2 O.sub.4 is quite small having a theoretical capacity of
only 148 mAh/g, and a practical capacity of typically less than
about 120 mAh/g. Further, the high charge voltage necessary for
materials such as LiMn.sub.2 O.sub.4 is near the potential at which
electrolyte decomposition occurs. Accordingly, a slight overcharge
may result in a significant electrolyte decomposition, and hence a
significant decrease in battery performance.
Lithiated high capacity manganese oxides have been known for a
number of years. For example, Li.sub.2 O stabilized,
gamma--MnO.sub.2 can be electrochemically lithiated to form
rechargeable LiMnO.sub.2 (as in the case of an unlithiated
MnO.sub.2 discharged in a battery). This process is described in a
pair of papers entitled "Preparation of High Surface Area EMD and
Three-Volt Cathode of Manganese Oxide," by M. Yoshio presented at
the IBA New Orleans Meeting of Oct. 9-10, 1993; and "Commercial
Cells Based on MnO.sub.2 and MnO.sub.2 -Related Cathodes", by T.
Nohma et al, in a publication entitled Lithium Batteries, edited by
G. Pistoia, and published by Elsevier Press. These materials have
been demonstrated to have a rechargeable capacity greater than 200
mAh/g at potentials higher than 2.5 volts but lower than 4 volts.
Unfortunately, unlithiated manganese oxides as the positive
material are less attractive than lithiated manganese oxides, as
discussed earlier. Further, electrochemical lithiation as described
in these papers is economically unfeasible at an industrial scale.
Therefore, a chemical process for synthesis of a low voltage, high
capacity lithiated manganese oxide is highly desirable. A lithiated
three-volt manganese oxide which has the formula LiMnO.sub.2 is
highly desirable as it possesses the advantages of both the
existing four and three-volt manganese oxide. Such a material,
prepared by an ion exchange method, was described by Ohzuku, et al
in a publication entitled Chemistry Express, 7, 193 (1992). This
material has been commented on extensively in subsequent papers
such as the M. Yoshio paper referenced above, and in a publication
entitled "Understanding the Disordered Structure LiMnO.sub.2
Prepared at Low Temperatures" by Reimers, et al. and appearing in
the Journal Chemical Physics.
Unfortunately, the ion-exchange process described by Ohzuku, et al
is both inefficient and does not lead to reproducible results, as
the authors themselves acknowledge. Moreover, the ion-exchange
process is not readily conducive to industrial scale manufacturing
in commercial quantities.
Accordingly, there exists a need for a simple method by which to
manufacture lithiated manganese oxide materials, such as
LiMnO.sub.2. The manufacturing process should be relatively simple,
take advantage of low-cost materials, and assure high repeatability
and reproducibility of material characteristics fabricated
accordingly to the process.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of an electrochemical cell
including a lithiated transition metal oxide electrode in
accordance with the instant invention;
FIG. 2 is a flow chart illustrating the steps for preparing a
lithiated transition metal oxide material in accordance with the
instant invention;
FIG. 3 is a charge and discharge profile for a LiMnO.sub.2
electrode vs. lithium, fabricated in accordance with the instant
invention;
FIG. 4 is a charge and discharge profile for a LiMnO.sub.2
electrode vs. graphite, fabricated in accordance with the instant
invention; and
FIG. 5 is a charge and discharge profile for a Li.sub.0.95
N.sub.0.05, MnO.sub.2 electrode vs. lithium metal, fabricated
according to the instant invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
While the specification concludes with claims defining the features
of the invention that are regarded as novel, it is believed that
the invention will be better understood from a consideration of the
following description in conjunction with the drawing figures, in
which like reference numerals are carried forward.
Referring now to FIG. 1, there is illustrated therein a schematic
representation of an electrochemical cell (10) including a
lithiated first transition metal oxide in accordance with the
instant invention. The electrochemical cell includes a positive
electrode (20) and a negative electrode (30) and has an electrolyte
(40) disposed therebetween. The cell positive electrode (20) is
fabricated of a three-volt alkaline metal transition metal oxide
charge storage material such as that described in greater detail
hereinbelow. The negative electrode (30) of the cell (10) may be
fabricated from a lithium alloying metal such as Al, Bi, Cd, or a
lithium intercalation material such as carbon, graphite, and other
such materials as are known in the art. Thus, the instant invention
allows the electrochemical cell to be assembled without relying
upon a metallic lithium or lithium alloy negative electrode.
The electrolyte (40) disposed between the electrode may be any of
the electrolytes known in the art including for example,
LiClO.sub.4 in propylene carbonate or polyethylene oxide
impregnated with a lithiated salt. The electrolyte (40) may also
act as a separator between the positive and negative
electrodes.
In accordance with the instant invention, there is provided a
method for synthesizing an alkaline transition metal oxide material
which is capable of storing and discharging electrical charge. The
material disclosed herein is therefore useful as, for example, a
cathode in lithium rechargeable batteries. The charge storage
material has the formula A.sub.x TmO.sub.2 where A is an alkaline
metal selected from the group of lithium, sodium, potassium, and
combinations thereof; Tm is a first transition metal selected from
the group of titanium, vanadium, manganese, chromium, iron, nickel,
cobalt and combinations thereof; and x is between 0.5 and 1.2.
Referring now to FIG. 2, there is illustrated therein a flow chart
describing the steps for preparing the alkaline metal transition
metal oxide in accordance with the instant invention. The first
step illustrated in the flow chart (70) is disclosed in box (72)
and includes the step of providing a first transition metal
hydroxide of the formula Tm(OH).sub.2. In one preferred embodiment
of the instant invention, the transition metal is provided in the
2+ oxidation state. Further, the transition metal may preferably be
manganese. Typically, the transition metal hydroxide must be
fleshly prepared as such materials are not typically stable in air
and may be easily decomposed into other products. For example,
manganese hydroxide, Mn(OH).sub.2 will easily decompose into MnO
and H.sub.2 O or be oxidized by O.sub.2 in the air into Mn.sub.2
O.sub.3. Mn(OH).sub.2 may be prepared from a manganese containing
salt such as Mn(NO.sub.3).sub.2, MnSO.sub.4, MnCO.sub.3,
Mn(CH.sub.3 CO.sub.2).sub.2, and combinations thereof, in an inert
environment by preparing a desired amount of, for example,
Mn(NO.sub.3).sub.2 dissolved in deionized water purged with
nitrogen gas. Thereafter, an alkaline metal hydroxide solution,
such as LiOH, NaOH, KOH, or others, is added to the manganese
containing salt described above, so that the manganese and lithium
are present in a ration of 1:2. Adding the alkaline metal hydroxide
causes a Mn(OH).sub.2 precipitate to form. The solution has a pH of
approximately 10. Thereafter, the precipitate is filtered in an
inert environment and dried under vacuum.
Returning to FIG. 2, the second step in the fabrication of the
alkaline metal transition metal oxide charge storage material is
illustrated in box (74) thereof. The second step includes reacting
the transition metal hydroxide material with a alkaline
metal-containing oxidizing agent, or a mixture of an alkaline
metal-containing salt and an oxidizing agent to form a mixture. The
alkaline metal-containing oxidizing agent may contain an alkaline
metal selected from the group of lithium, sodium, potassium, and
combinations thereof. Exemplary materials which may be used as the
alkaline metal containing oxidizing agent include lithium peroxide
(Li.sub.2 O.sub.2), lithium nitrate (LiNO.sub.3), LiClO.sub.4,
Na.sub.2 O.sub.2, K.sub.2 O.sub.2, and combinations thereof.
The transition metal hydroxide and the alkaline metal containing
oxidizing agent should be mixed so that the ratio of transition
metal to alkaline metal is between 0.5:1 and 1.2:1. The mixing is
preferably carried out in the presence of an organic solvent having
a relatively low boiling point. Examples of such a solvents include
acetone, acetonitrile, and tetrahydrofuran to name a few. After
thorough mixing, the organic solvent may be removed, yielding a
powdered alkaline metal, transition metal oxide. The resulting
mixture may thereafter be dried in an inert environment for several
hours. This step is illustrated in Box 76 of FIG. 2. The materials
may optionally be calcined at temperatures of up to 800.degree. C.
for several hours in an inert gas environment, as illustrated in
box 78 of FIG. 2.
The invention may be better understood from the examples presented
below.
EXAMPLES
Example I
A first sample of the alkaline metal transition metal, oxide charge
storage material was made according to the instant invention. The
starting transition metal hydroxide was manganese hydroxide
Mn(OH).sub.2. Lithium peroxide Li.sub.2 O.sub.2 was employed as the
alkaline metal containing oxidizing agent. Manganese hydroxide was
prepared by dissolving 18 grams of Mn(NO.sub.3).sub.2.6 H.sub.2 O
in 200 milliliters of deionized water purged with nitrogen gas.
Thereafter, a 1M solution of lithium hydroxide (LiOH) was added to
the manganese containing solution. The ratio of manganese to
lithium in the solution was approximately 1:2. The solution so
formed provided an Mn(OH).sub.2 precipitate. The Mn(OH).sub.2 was
filtered from the solution in an inert environment. The precipitate
was then dried under vacuum. The precipitate was then thoroughly
mixed with 1.4 g of lithium peroxide. The ratio of manganese to
lithium in this second mixture was approximately 1:1. Mixing took
place in a ball mill mixer in the presence of 60 ml of
tetrahydrofuran (THF). The mixture was then dried further and
heated to 450.degree. C. in an nitrogen atmosphere for a period of
30 hours.
The resulting powder had the composition of LiMnO.sub.2. A mixture
of the LiMnO.sub.2 powder along with graphite powder (10 wt/%) and
PTFE (Teflon), powder (5 wt/%) was fabricated into a thin sheet via
conventional processes. A 1 cm.sup.2 sample having a thickness of
approximately 60 .mu.m was cut from the sheet and tested as the
positive lithium intercalation electrode in a test cell. The test
cell further included a glass mat as the separator and a lithium
foil as the negative electrode. The electrolyte was 1M LiPF.sub.6
in a solution of 50% ethylene carbonate and 50% dimethyl carbonate.
Tests were carried out at ambient temperatures (approximately
22.degree. C.).
Referring now to FIG. 3, there is illustrated therein a typical
charge/discharge profile of cell voltage for the sample described
above. The first charge profile (as the material is fabricated in
an uncharged condition) is shown on line 80, the first discharge on
line 82, and the second charge on line 84. It may be appreciated
that a capacity as high as approximately 210 mAh/g has been
obtained. It is hypothesized that since Li.sub.2 O.sub.2 partially
decomposes into Li.sub.2 O and O.sub.2 during mixing with
Mn(OH).sub.2 and thus the reaction between Li.sub.2 O.sub.2 and
Mn(OH).sub.2 may not be complete. Thus, the original product
obtained contains some amounts of electrochemically inactive
materials such as Li.sub.2 O and MnO. When these electrochemically
inactive materials are removed by conventional washing methods, the
capacity of the material is expected to exceed 210 mAh/g. FIG. 3
shows that high capacities may be achieved in materials fabricated
by this method, and further that the materials may be repeatably
cycled.
Referring now to FIG. 4, there is illustrated therein a
charge/discharge profile of cell voltage for an electrochemical
cell including the LiMnO.sub.2 positive electrode fabricated
according to the method described hereinabove and a graphite
negative electrode. The mass ratio of the positive to the negative
was approximately 2.3:1. The first charge is illustrated on line
86, while the first discharge and second charge are shown on line
88 and 90. From a perusal of FIG. 4, it may be appreciated that
despite a significant capacity loss due to the graphite electrode,
a capacity greater than approximately 150 mAh/g has been obtained.
By way of comparison for the same mass ratio, the practical
capacity of the positive material would be less than 80 mAh/g if
conventional LiCO.sub.2 or LiM.sub.2 O.sub.4 is used as the
positive material.
Example 2
Providing Mn(OH).sub.2 prepared in a method as described
hereinabove in Example 1, such material was then mixed thoroughly
with Na.sub.2 O.sub.2 and Li.sub.2 O.sub.2 in the molar ratio: Na:
Li: Mn=0.05:0.95:1, in the presence of THF. The mixture was dried
at ambient temperatures under vacuum and then heated to
approximately 450.degree. C. in a nitrogen atmosphere for
approximately 30 hours. The final product had a formula of
Li.sub.0.95 Na.sub.0.05 MnO.sub.2.
The resulting powder was mixed along with carbon black (10 wt/%)
and PTFE (Teflon) powder (5 wt/%) and fabricated into a thin sheet
via conventional processing. A 1 cm.sup.2 sample having a thickness
of approximately 60 microns was cut from the sheet and tested as
the positive electrode in a cell with lithium foil as the
counterelectrode. The test cell further included a glass mat
separator, and a 1M LiPF.sub.6 electrolyte in a solution of 50%
ethylene carbonate and 50% dimethylcarbonate.
Referring now to FIG. 5, there is illustrated therein a
charge/discharge profile of cell voltage for the material
fabricated according to this example. From a perusal of FIG. 5 it
may be appreciated that a capacity of as high as 250 mAh/g was
obtained. Moreover, cycleability is demonstrated, since the
material shows similar characteristics from the first charge 92 to
the second charge 96. Line 94 illustrated the first discharge.
While the preferred embodiments of the invention have been
illustrated and described, it will be clear that the invention is
not so limited. Numerous modifications, changes, variations,
substitutions and equivalents will occur to those skilled in the
art without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *